Hydraulic fracture composition and method

ABSTRACT

A method for improving the performance of fracturing processes in oil production fields may rely on polymer coated particles carried in the fracturing fluid. The particles may include heavy substrates, such as sand, ceramic sand, or the like coated with polymers selected to absorb water, increasing the area and volume to travel more readily with the flow of fluid without settling out, or allowing the substrate to settle out. Ultimately, the substrate may become lodged in the fissures formed by the pressure or hydraulic fracturing, resulting in propping open of the fissures for improved productivity.

RELATED APPLICATIONS

This application: is a divisional of U.S. patent application Ser. No.16/390,559, filed Apr. 22, 2019; which is a divisional of U.S. patentapplication Ser. No. 14/171,920, filed Feb. 4, 2014; which is acontinuation of U.S. patent application Ser. No. 13/418,227, filed Mar.12, 2012; which is a continuation-in-part of U.S. patent applicationSer. No. 13/299,288, filed Nov. 17, 2011; which is acontinuation-in-part of U.S. patent application Ser. No. 12/789,177,filed May 27, 2010, now U.S. Pat. No. 8,341,881 issued Jan. 1, 2013;which is a continuation of U.S. patent application Ser. No. 12/324,608,filed on Nov. 26, 2008 now U.S. Pat. No. 7,726,070, issued Jun. 1, 2010;which claims the benefit of U.S. Provisional Patent Application Ser. No.61/012,912, filed Dec. 11, 2007; all of which are hereby incorporated byreference in their entirety.

BACKGROUND 1. The Field of the Invention

This invention relates to oil field and oil well development, and, moreparticularly, to novel systems and methods for fracturing and proppingfissures in oil-bearing formations to increase productivity.

2. The Background Art

Oil well development has over one hundred years of extensive engineeringand chemical improvements. Various methods for stimulating production ofwell bores associated with an oil reservoir have been developed. Forexample, United States Patent Application Publication US 2009/0065253 A1by Suarez-Rivera et al. and entitled “Method and System for IncreasingProduction of a Reservoir” is incorporated herein by reference in itsentirety and provides a description of fracturing technology in order toincrease permeability of reservoirs. Moreover, various techniques existto further improve the fracture channels, such as by acid etching asdescribed in U.S. Pat. No. 3,943,060, issued Mar. 9, 1976 to Martin etal., which is likewise incorporated herein by reference in its entirety.

In general, different types of processes require various treatments. Ingeneral, well production can be improved by fracturing formations.Fracturing is typically done by pumping a formation full of a fluid,containing a large fraction of water, and pressurizing that fluid inorder to apply large surface forces to parts of the formation. Theselarge surface forces cause stresses, and by virtue of the massive areasinvolved, can produce extremely high forces and stresses in the rockformations. Accordingly, the rock formations tend to shatter, increasingporosity an providing space for the production oil to pass through theformation toward the bore hole for extraction. However, as the foregoingreferences describe, the chemistry is not simple, the energy and timerequired for incorporation of various materials into mixtures is time,money, energy, and other resource intensive.

It would be an advance in the art if such properties as viscosity,absorption, mixing, propping, and so forth could be improved by animproved composition and method for introduction.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, in accordance with the invention as embodiedand broadly described herein, a method, apparatus, and composition aredisclosed in certain embodiments in accordance with the presentinvention, as including a substrate that may be formed of sand, rockproduct, ceramic sand, gravel, or other hard and structurally strongmaterials, provided with a binder to temporarily or permanently secure ahydrating polymer in proximity to the substrated. When used herein anyreference to sand or proppant refers to any or all of these used inaccordance with the invention. In certain embodiments of a method inaccordance with the invention, a composition as described may be mixeddirectly into drilling fluids, such as a fracturing fluid made up ofwater and other additives.

By virtue of the increased surface area and weight provided to thepolymeric powders affixed to the substrate, the surface area, andconsequently the frictional drag, is greatly increased, sweeping thematerial of the invention into a flow of fluid. This greatly decreasesthe time required to absorb polymers into the fluid.

In fact, rather than having to wait to have the polymers thoroughlymixed, or absorb a full capacity of water, and thereby flow properlywith the drilling fluid or fracturing fluid, a composition in accordancewith the invention will sweep along with the fluid immediately, with theweight of the substrate submerging the polymer. Meanwhile, the crosssectional area presented results in hydrodynamic drag sweeps thecomposition along with the flow.

Meanwhile, over time, the polymeric powder adhered to the substrate willabsorb water, without the necessity for the time, energy, temperature,mixing, and so forth that might otherwise be required by surface mixing.Thus, the composition in accordance with the invention is immediatelytransportable and flows, relying on the drilling or fracturing fluid asits carrier.

Moreover, as the polymer tends to pick up more water, the density of thegranule of substrate and polymer powder becomes closer to the density ofwater. Accordingly, the size increase and the density change tend todrive the particles of the composition even more homogeneously with theflowing fluid. Thus, the sand does not settle out in various eddies,obstructions, and other locations of low velocity. Rather, the sandcontinues to be carried with the fluid, providing a double benefit. Thatis, the sand weight and area helps to initially mix and drive theparticles (granules) with the fluid. Thereafter, the hydration of thepolymer tends to increase the surface area and reduce the density of thegranule or particle, tending to make the particles flow even better andmore homogeneously with the surrounding fluid.

Ultimately, as the particles (granules) of the composition flow intofracture locations, they provide very small proppants as the substrate,such as sand, becomes trapped and lodged at various choke points.Nevertheless, because of the small size, the sand or other substrateacting as a proppant, simply needs to provide an offset, keepingfractured surfaces from collapsing back against one another. Byproviding the small, strong points of separation, the substrate providesa well distributed proppant, carried to maximum extent that the fluidswill travel, and deposited in various traps, choke points, and the like.

The net saving in time, money, energy for heating and pumping, and thelike is significant. Meanwhile, various technologies for reducingfriction in the flow of fluid pumped into bore holes and other formationspaces is described in several patents, including U.S. Pat. No.3,868,328, issued Feb. 25, 1975 to Boothe et al. and directed tofriction reducing compounds, as well as U.S. Pat. No. 3,768,565, issuedOct. 30, 1973 to Persinski et al. and directed to friction reducing,U.S. Patent Application Publication US 2001/0245114 A1 by Gupta et al.directed to well servicing fluid, and U.S. Patent ApplicationPublication US 2008/0064614 A1 by Ahrenst et al. and directed tofriction reduction fluids, all described various techniques, materials,methods, and apparatus for developing, implementing, and benefittingfrom various well fluids. All the foregoing patent applicationpublications and patents are hereby incorporated by reference.

Similarly, the development of various chemicals has been ubiquitous inoil field development. For example, U.S. Pat. No. 3,442,803, issued May6, 1969 to Hoover et al. is directed to thickened friction reducers,discusses various chemical compositions, and is also incorporated hereinby reference in its entirety.

In one embodiment of an apparatus, composition and method in accordancewith the invention, a method may be used for formation fracturing. Theformation may be in rock and within or near an oil reservoirunderground. One may select an oil field region having a formation to befractured. Fracturing may be sought to increase production. By providinga bore into the formation and a pump, a carrier material, typicallycomprising a liquid, and sometimes other materials dissolved or carriedtherein may be pumped into the formation through the bore.

The carrier as a liquid, or slurry comprising a liquid, or otherwisecontaining a liquid may be driven by the pump to be pressurized into theformation. However, the carrier may be provided an additive formed asgranules. Each granule may include a substrate, such as a grain of sand,ceramic sand, crushed rock, other rock products, or the like havingbonded thereto many particles (e.g. powder) formed from a polymer.

The polymer may be selected to have various properties, includinglubricity, water absorption, water solubility, or the like. Thishydrophilic polymer may be bonded permanently, temporarily, or the liketo secure to the substrate. Various binders may be used alone or incombination. These may range from a solvent (e.g., organic or water)simply softening the polymer itself to bond it, to glues, sugars,molasses, and various other saccharides, as well as other products,including starches, other polymers, and so forth.

Thus, with some bonds, the polymer powder may be less permanent orattached to have a bond that is less robust. Over time, the polymerpowder so attached may wear off, pull away, or otherwise remove from thesubstrate into the carrier fluid, and may even act as a viscous agent,lubricant, or the like in the carrier.

The method may include introducing the additive directly into thecarrier. The more dense substrate will immediately submerge the granulesin the carrier at ambient conditions. Thus heating, extensive mixing,waiting, and the like may be dispensed with, as the granules typicallywill not float or resist mixing once initial surface tension is broken.

Pumping the carrier toward the formation is possible immediately. Thecarrier fluid carries the granules by the liquid dragging against thesubstrate (with the particles of polymer attached. The substrate's crosssectional area engages immediately the surrounding liquid, dragging itinto the carrier to flow substantially immediately therewith.

Meanwhile, weighting, by the substrate of the polymer, permits thegranules to flow into and with the carrier independently from absorptionof any of the liquid into the polymer. Nevertheless, over time,absorbing by the polymer a portion of the liquid results in the polymerexpanding and providing by the polymer, lubricity to the carrier withrespect to the formation;

Creating fractures may be accomplished by pressurizing the carrier inthe formation. This creates fissures or fractures. Thus, flowing of thecarrier and particles throughout the fractures or fissures in theformation results in lodging, by the particles, within those fracturesor fissures. Unable to re-align, adjacent surfaces of rock, now fracturecannot close back together due to propping open the fractures by thesubstrate granules lodging in the fractures.

The substrate is best if selected from an inorganic material, such assand, ceramic sand, or other hard, strong, rock product. The polymer maybe selected from natural or synthetically formulated polymers. Forexample polymers of at acrylic acid, acrylate, and various amides areavailable. Polyacrylamide has been demonstrated suitable for allproperties discussed above.

In fracturing a rock formation, the method may include providing anadditive comprising a substrate formed as granules, each having anexterior surface, particles formed of a hydrophilic material, theparticles being comminuted to a size smaller than the size of thegranules and having first and second sides comprising surfaces. Thegranules may each be coated with the particles, the particles being dryand bonded to the exterior surface by any suitable binder, including thepolymer softened with a solvent. The particles are each secured by thefirst side to the granules, the second side extending radially outwardtherefrom.

Upon identifying a reservoir, typically far underground from thousandsof feet to miles, perhaps, and extending in a formation of rock, oneneeds to provide a bore into the formation. Providing a carrier,comprising a liquid, and possibly other materials known in the art, isfor the purpose of fracturing the formation. Introducing the additivedirectly into the liquid at ambient conditions is possible, because thesubstrate weighs the granules down, and there is no need for longmixing, heating or the like as in addition of polymers directly to thecarrier.

Thus, pumping may continue or begin immediately to move the carrier andadditive down the bore and toward the formation. This results inexposing the second sides of the polymer powder particles directly tothe liquid during transit of the carrier and additive toward and intothe formation. The polymer particles thus begin absorbing, a portion ofthe liquid, typically principally water. Swelling of the polymerincreases the size, effective diameter, and cross-sectional area, thusincreasing the fluid drag on the granules.

Fracturing, typically by hydraulic pressure in the carrier createsfissures in the formation by fracturing the rock pieces in bending, orby layer separation, with tensile stresses breaking the rock. Theresulting fissures allow carrying, by the carrier, of the granules intothe fissures. However, fissures vary in size and path, resulting inlodging of granules, within the fissures. The granules do not settle outfrom the carrier, and thus may travel far into the formation and everyfissure. However, each time a grain or granule is lodged like a chockstone, it obstructs the ability of the adjacent rock surfaces to closeback with one another.

Thus, rather than the proppant (substrate) settling out ineffectually,failing to prop open the fissures, the granules are swept forcefullywith the flow of the carrier wherever the carrier can flow, untillodged. Meanwhile, the lubricity of the polymer aids the granules, andthus the substrate from being slowed, trapped, or settled out by theslow flowing boundary layer at the solid wall bounding the flow.

In summary, weighting, by the substrate, sinks the polymer into thecarrier readily and independently from absorption of the liquid into thepolymer. Mixing, dissolving, and so forth are unnecessary, as thesubstrate drags the polymer into the carrier, and the carrier drags thegranule along with it in its flow path. Lubrication is provided by thepolymer between the substrate of each granule and adjacent solid wallsof the bore, passages previously existing in the formation, and thefissures formed by fracturing. Any separating, by some of the powderedpolymer particles from the substrate, still reduces friction drag onpassage of the carrier and particles within the formation.

A composition for fracturing and propping a formation of rock mayinclude a fluid operating as a carrier to be pumped into a rockformation, a substrate comprising granules of an inorganic material,each granule having an outer surface and a size characterized by amaximum dimension thereacross, and all the granules together having anaverage maximum dimension corresponding thereto. A polymer comprising ahydrophilic material selected to absorb water in an amount greater thanthe weight thereof may be bound to the substrate. The polymer iscomminuted to particles, each particle having a size characterized by amaximum dimension thereacross.

All the polymer particles may be characterized by an average maximumdimension, and an effective (e.g. hydraulic diameter). The averagemaximum dimension of the particles is best if smaller, preferably muchsmaller, than the average maximum dimension of the granules.

The particles of the polymer, bound to the substrate, will travel withit in the fluid. Particles of the polymer are thus further directlyexposed to water in the fluid during travel with the fluid. Thegranules, flowing in the fluid, are carried by the hydrodynamic drag ofthe fluid against the cross-sectional area of the granules coated withthe particles of the polymer. The polymer, selected to expand byabsorbing water directly from the fluid, increases the area and drag,assisting distribution in the formation by the carrier fluid. Thepolymer meanwhile operates as a lubricant lubricating the motion of thesubstrate against the formation during flow of the granules againstsolid surfaces in the formation, bore, and fracture fissures.

The inorganic material, such as sand, ceramic sand, or the like istypically sized to lodge in fissures formed in the formation and hasmechanical properties rendering it a proppant capable of holding openfissures formed in the formation.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the present invention will become more fullyapparent from the following description and appended claims, taken inconjunction with the accompanying drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are,therefore, not to be considered limiting of its scope, the inventionwill be described with additional specificity and detail through use ofthe accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view of a material including asubstrate provided with a binder securing a hydrating polymer thereto inaccordance with the invention;

FIG. 2 is a schematic block diagram of one embodiment of a process forformulating and producing fluid additive particles in accordance withthe invention;

FIG. 3 is a schematic diagram of the fluid-particle interaction in anapparatus, composition, and method in accordance with the invention;

FIG. 4 is a chart illustrating qualitatively the relationship betweenvolumetric increase over time at various temperatures, illustrating theimproved activation with minimum mixing and temperature increase ofparticles in accordance with the invention;

FIG. 5 is a schematic diagram illustrating one embodiment of frictionreducing by polymers used in compositions in accordance with theinvention;

FIG. 6 is a schematic diagram of the fracturing and proppant action ofparticles in accordance with a method and composition according to theinvention; and

FIG. 7 is a schematic block diagram of a fracturing and propping processusing compositions and methods in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the drawingsherein, could be arranged and designed in a wide variety of differentconfigurations. Thus, the following more detailed description of theembodiments of the system and method of the present invention, asrepresented in the drawings, is not intended to limit the scope of theinvention, as claimed, but is merely representative of variousembodiments of the invention. The illustrated embodiments of theinvention will be best understood by reference to the drawings, whereinlike parts are designated by like numerals throughout.

Referring to FIG. 1, a material 10 in accordance with the invention mayinclude a substrate 12 formed of a suitable material for placement inthe vicinity of a fracture region. For example, a substrate may be aparticle of sand, ceramic sand, volcanic grit, or other hard material.In some embodiments, a substrate may be formed of organic or inorganicmaterial. Nevertheless, it has been found effective to use sand as asubstrate 12 inasmuch as it is submersible in water and will not floatas many organic materials will when dry. Likewise, the sand as substrate12 is comminuted to such a small size that interstices betweenindividual grains of the sand substrate 12 provide ample space andminimum distance for water to surround each of the substrate 12particles.

In the illustrated embodiment, a binder 14 may be distributed as acomparatively thin layer on the surface of the substrate 12. Typicalmaterials for binders may include both temporary and permanent binders14. Permanent binders include many polymers, natural and synthetic.Temporary binders may be sugar-based or other water soluble materials.For example, corn syrup, molasses, and the like may form temporarybinders. In the presence of water, such material may ultimatelydissolve. Nevetheless, so long as the substrate 12 is not turned, mixed,or otherwise disturbed significantly, any other materials supported bythe binder 14 would not be expected to dislocate.

Otherwise, certain naturally or synthetically occurring polymers mayalso be used as a binder 14. Lignicite may be used as a binder 14.Lignicite is a byproduct of wood, and provides material having goodadhesive properties, and substantial permanence as a binder 14 on asubstrate 12. Any suitable insoluble polymer may be used for morepermanent binding.

Other polymers may be used to form a binder 14. For example, variousmaterials used as glues, including mucilage, gelatin, other watersoluble polymers including, for example, Elmer's™ glue, and the like mayalso operate as binders 14 to bind materials to a substrate 12.

In certain embodiments, the substrate 12 may be used in oil fields as asubstrate 12 for polymer additives to fracture fluids. In othersituations, the substrate 12 may be implemented as a proppant.

Pigment 16 may be implemented in any of several manners. For example,the substrate 12 may have pigment 16 applied prior to the application ofthe binder 14. In alternative embodiments, the pigment 16 may actuallybe included in the binder 14, which becomes a pigmented coating on thesubstrate 12. In yet other embodiments, the pigments 16 may be added toa hydration particle 18 either as a pigment 16 mixed therein, or as apigment 16 applied as a coating thereto. Thus the location of thepigment 16 in the Figures is schematic and may take alternative locationor application method.

Particles 18 of a hydrophilic polymer material may be bonded to thesubstrate 12 by the binder 14. Particles may be sized to substantiallycoat or periodically coat the substrate 12.

In certain embodiments, the hydrophilic material 18 may be a powderedpolymeric material 18 such as polyacrylamide or any of the materials inthe patent documents incorporated by reference. In other embodiments,the particles 18 may actually be organic material having capillaryaction to readily absorb and hold water. In one presently contemplatedembodiment of an apparatus in accordance with the invention, theparticles 18 may be powdered polymeric material in a dehydrated state,and having a capacity to absorb water, typically many times the weight(e.g., five to forty times) of a particular particle 18.

The substrate 12, in certain embodiments, may be some form of sand orgrannular material. The sand will typically be cleaned and washed toremove dust and organic material that may inhibit the binder 14 frombeing effective. Likewise, the substrate 12 may be sized of any suitablesize. For example, sand particles may range from much less than amillimeter in effective diameter or distance thereacross toapproximately two millimeters across. Very coarse sands or ceramic sandsmay have even larger effective diameters. Hydraulic diameter iseffective diameter (four times the area divided by the wettedperimeter). However, in one presently contemplated embodiment, washedand dried sand such as is used in construction, such as in concrete, hasbeen found to be suitable. Fine sands such as masonry sands tend to besmaller, and also can function suitably in accordance with theinvention.

Accordingly, the distance across each powder particle 18 may be selectedto provide an effective coating of powdered particles 18 on thesubstrate 12. In one presently contemplated embodiment, the effectivediameter of the particles 18 may be from about a 30 mesh size to about a100 mesh size. For example, a sieve system for classifying particles hasvarious mesh sizes. A size of about 30 mesh, able to pass through a 30mesh sieve, (i.e., about 0.6 mm) has been found suitable. Likewise,powdering the particles 18 to a size sufficiently small to pass througha 100 mesh (i.e., about 0.015 mm) sieve is also satisfactory. A meshsize of from about 50 mesh to about 75 mesh is an appropriate materialto obtain excellent adhesion of particles 18 in the binder 14, with asuitable size of the particles 18 to absorb significant liquid at thesurface of the substrate 12.

As a practical matter, about half the volume of a container containing asubstrate 12 as particulate matter will be space, interstices betweenthe granules of the substrate 12. One advantage of using materials suchas sand as the substrate 12 is that a coating of the particles 18 mayprovide a substantial volume of water once the particles 18 are fullysaturated. By contrast, where the size of the particles 18 is too manyorders of magnitude smaller than the effective diameter or size of thesubstrate particles 12, less of the space between the substrateparticles 12 is effectively used for storing water. Thus, sand as asubstrate 12 coated by particles 18 of a hydrophilic material such as apolymer will provide substantial space between the substrate particles12 to hold water-laden particles 18.

The diameter of the particles 18, or the effective diameter thereof, istypically within about an order of magnitude (e.g., 10×) smaller thanthe effective diameter of the particles of the substrate 12. This orderof magnitude may be changed. For example, the order of magnitudedifference less than about 1 order of magnitude (i.e., 10×) may still beeffective. Similarly, an order of magnitude difference of 2 (i.e., 100×)may also function.

However, with particles 18 too much smaller than an order of magnitudesmaller than the effective diameter of the substrate 12, theinterstitial space may not be as effectively used. Likewise, with aneffective diameter of particles 18 near or larger than about 1 order ofmagnitude smaller than the size of the particles of the substrate 12,binding may be less effective and the particles 18 may interfere morewith the substrate itself as well as the flow of water through theinterstitial spaces needed in order to properly hydrate a material 10.

Referring to FIG. 2, an embodiment of a process for formulating thematerial 10 may involve cleaning 22 the material of the substrate 12.Likewise, the material of the substrate 12 may be dried 24 to make itmore effective in receiving a binder 14. The material of the substrate12 may then be blended 26.

One embodiment, a ribbon blender provides an effective mechanism toperform continuous blending as the binder 14 is added 28. Other types ofmixers, such as rotary mixers, and the like may be used. However, aribbon blender provides a blending 26 that is effective to distributebinder 14 as it is added 28.

For example, if an individual particle of the substrate 12 receives toomuch binder 14, and thus begins to agglomerate with other particles ofthe substrate 12, a ribbon binder will tend to separate the particles asa natural consequences of its shearing and drawing action duringblending 26.

As the binder 14 is added 28 to the mixture being blended 26, theindividual particles of the substrate 12 will be substantially evenlycoated. At this stage, the binder 14 may also be heated in order toreduce its viscosity and improve blending. Likewise, the material of thesubstrate 12 or the environment of the blending 26 may be heated inorder to improve the evenness of the distribution of the binder 14 onthe surfaces of the substrate 12 materials or particles 12.

Blending 26 of the binder 14 into the material of the substrate 12 iscomplete when coating is substantially even, and the texture of thematerial 10 has an ability to clump, yet is easily crumbled and brokeninto individual particles. At that point, addition 30 of the hydrophilicparticles 18 may be accomplished.

For example, adding 30 the particles 18 as a powder into the blending 26is a naturally stable process. Typically the particles 18 attach to thebinder 14 of the substrate 12 particles, thus removing from activitythat location. Accordingly, other particles 18 rather than agglomeratingwith their own type of material will continue to tumble in the blending26 until exposed to a suitable location of binder 14 of the substrate12. Thus, the adding 30 of the particles 18 or powder 18 of hydrophilicmaterial will tend to be a naturally stable process providing asubstantially even coating on all the particles of the substrate 12.

Just as marshmallows are dusted with corn starch, rendering them nolonger tacky with respect to one another, the material 10 formulated bythe process 20 are dusted with particles 18 and will pour freely.Accordingly, distribution 32 may be conducted in a variety of ways andmay include one or several processes. For example, distribution mayinclude marketing distribution from packaging after completion ofblending 26, shipping to distributers and retailers, and purchase andapplication by users.

An important part of distribution 32 is the deployment of the material10. In one embodiment of an apparatus and method in accordance with theinvention, the material 10 may be poured, as if it were simply sand 12or other substrate 12 alone. Since the powder 18 or particles 18 havesubstantially occupied the binder 14, the material 10 will not bind toitself, but will readily pour as the initial substrate material 12 will.

The material 10 may typically include from about 1 percent to about 20percent of a hydrophilic material 18 or particles 18. The particles 18may be formed of a naturally occurring material, such as a cellulose,gelatin, organic material, or the like.

In one embodiment, a synthetic gel, such as polyacrylamide may be usedfor the particles 18, in a ratio of from about 1 to about 20 percentparticles 18 compared to the weight of the substrate 12. In experiments,a range of from about 5 to about 10 percent has been found to be themost effective for the amount particles 18.

Sizes of particles 18 may range from about 20 mesh to smaller than 100mesh. Particles 18 of from about 50 to about 75 mesh have been foundmost effective.

The binder 14 may typically be in the range of from about in ¼ percentto about 3 percent of the weight of the substrate 12. A range of fromabout ¾ percent to about 1½ percent has been found to work best. Thatis, with a binder such as lignicite, ¼ of 1 percent has been found notto provide as reliable binding of particles 18 to the substrate 12.Meanwhile, a ratio of higher than about 3 percent by weight of binder 14to the amount of a substrate 12, such as sand, when using lignicite asthe binder 14, tends to provide too much agglomeration. The pouringability of the material 10 is inhibited as well as the blending 26, dueto agglomeration. Other binders also operate, including several smallermolecules that are water soluble. For example, glues, gelatins, sugars,molasses, and the like may be used as a binder 14. Insoluble binders arealso useful and more permanent.

One substantial advantage for the material 10 in accordance with thepresent invention is that the material remains flowable as a sand-likematerial 10 into the fluids to be used in oil field fracturing. Thus,handling and application is simple, and the ability of granular material10 to flow under and around small interstices of fractures provides fora very effective application.

Referring to FIG. 3, a formation 80 such as a reservoir area of an oilmay increase large and small flows 82 in passages 84 formed in the rock86 of the formation 80. Typically, the flow 82 represented by arrows 82indicating the development of flow at a faster speed in center of apassage 84, and the lower velocity near the wall 88 of the passage 84,illustrates the flow 82 of fluid in the passage 84.

In the illustrated embodiment, the granules 10 or large compositeparticles 10 or the materials 10 formed as a granulated material 10,having the substrate 12 in the center column with the polymer 18 adheredby a binder 12 on the outside thereof. This material 10 may be added toa flow 82 being pumped into a formation 80. Initially, a particle 10will have an effective diameter 90 a. In this condition, the particle 10of material 10 is largely dependent on the density of the substrate 12,which constitutes the majority of its volume. Eventually, over time,with exposure to the liquid 82 or flow 82 and the water of that flow 82,the polymer 18 will absorb water, increasing in its effective diameter90 b. Ultimately, the polymer 18 or the polymer powder 18 willeventually become fully hydrated, increasing many times its size, andbeginning to dominate the effective diameter 90 c or hydraulic diameter90 c of the particle 10.

Initially, the diameter 90 a reflects the comparatively smaller size andlarger density of the particle 10 dominated by the weigh of thesubstrate 12, such as sand, ceramic sand, or some other hard and strongmaterial. Ultimately, the diameter 90 a or effective diameter 90 a issufficient to provide fluid drag according to fluid dynamic equations,drawing the particle 10 into the flow 82.

Meanwhile, the increase in diameter 90 b and the ultimate effectivediameter 90 c result in reduction of the density of the particle 10 asthe polymer 18 absorbs more water, bringing the net density of theparticle 10 closer to the density of water. Accordingly, the particles10 flow with the water exactly in sync, so to speak, rather thansettling out as a bare substrate 12 would do.

For example, in areas where eddies in the flow occur, such as corners,crevices, walls, and the like, heavy materials having higher density,such as sand and the like, normally will tend to drift out of the flow,toward a wall 88, and ultimately will settle out. Instead, by virtue ofthe large “sail” presented by the larger diameter 90 c of a fullyhydrated polymer 18, each particle 10 stays with the flow 82 in passage84, providing much more effective transport.

Referring to FIG. 4, a chart 92 illustrates a volume axis 94representing the volume of a particle 10 or material 10 in accordancewith the invention. The volume axis 90 is displayed orthogonally withrespect to a time axis 96, representing the passage of time of theparticle 10 submerged in a carrier 82 or flow 82 of fluid 82. Typically,at different temperatures, illustrated by curves 98 a-98 e, with thetemperature associated with curve 98 a being the coldest and thetemperature associated with the curve 98 e being the hottest, one canvisualize how heat added to a fluid flow 82 tends to increase thechemical activity and thus the rate of absorption of water into apolymer 18.

In an apparatus and method in accordance with the invention, theparticles 10 may be added directly to a flow 82, without waiting for anysignificant time to absorb water into the polymer 18. Instead, thenormal flow 82 will draw the particles 10 along in a passage 84 whileexposing each individual particle 10 to surrounding fluid 82, thuspromoting maximum rates of exposure and increased rates of absorption.Accordingly, the volume 94 increases, representing an increase in theabsorption of water into the polymer 18.

In an apparatus and method in accordance with the invention, the curve98 a is suitable because the entire travel within the well bore, andwithin the formation 80 by the fluid 82 bearing the particles 10 ispermissible and available as absorption time. By contrast, prior artsystems rely on the increased temperature of curve 98 e in order toprovide the time, temperature, and mixing to work polymers into a flow82 or liquid carrier 82.

Referring to FIG. 5, in one embodiment of an apparatus, composition, andmethod in accordance with the invention, some of the polymer 18 mayeventually be scraped, sheared, or otherwise removed from the particles10. If bonded only by itself with a water solvent, such a separation maybe easier than if bonded by a more durable polymer. Such a release mayeven be engineered, timed, controlled by a solvent, or the like.

Thus, a certain amount of the polymer 18 may be released from thegranule 10 into the carrier fluid 82 to flow with the fluid 82 andoperate as a general friction reducer or provide its other inherentproperties to the carrier fluid 82. By an engineered process of bondingand un-bonding, the polymer powder may be less permanent or attached tohave a bond that is less robust. Over time, the polymer powder soattached may release, tear, wear off, pull away, or otherwise removefrom the substrate into the carrier fluid to act as a viscosity agent,surfactant, lubricant, or the like in the carrier, according to itsknown properties available for modifying the carrier 82.

For example, a polymer 100 or polymer chain 100 may be captured on acorner 102 defining a passage 84 into which a flow 82 will proceed.Accordingly, the corner 102 renders less of an orifice on the passage 84against entry of the flow 82 by virtue of the friction reduction of thepolymer 100 in the fluid, deposited temporarily or permanently about acorner 102. Thus, other particles 10 passing the corner 100 may shearoff a portion of the polymer 18 carried thereby or may rely on thepresence of the polymer 18 as a direct friction reducing agent on theparticle 10 (granule) itself, permitting the particles 10 to pass moreeasily with the flow 82 into the passage 84.

Referring to FIG. 6, the fracture process is described in variousliterature, including U.S. Patent Application publication US2009/0065253 by Suarez-Rivera et al. incorporated herein by reference.In a fracturing process, the pressure applied to a formation 80 tends toforce apart large expanses of rock. As a result of that expansion ofpassages 84 in a rock formation 80, the rock is stressed. Pressurepumped into the fluid 82 flowing in the passages 84 within the formation80 results in bending stresses, tensile stresses, and so forth in theformation 80.

In FIG. 6, the forces 110 illustrated the effect of a large pressureapplied over a large area. Since pressure multiplied by area equalsforce, applying an elevated hydraulic pressure to a large surface of arock 86 or rock segment 86 within a formation 80 results in tensileforces. Compressive forces will not tend to break rock. However, atensile force, which may be induced by bending, expansion, or the like,results in fracture of the rock. The fracture of the rock 86 thusresults in condition shown in the lower view, in which the passages 84are mere fissures within the rock 86.

The inset of FIG. 6 magnifies the fissures 84 or passages 84 formed inthe rock 86 and immediately entered by the working fluid 82 being usedfor the fracture. Having the particles 10 formed around substrates 12,the fluid 82 extends into each of the fissures formed. Fissures 84 aresimply passages 84. Some may be large, others small. Proppants 10trapped in a small location may still maintain opened in another openingmuch larger elsewhere on the rock 86. They may also collect and filllarger spaces, eliminating the ability for rocks 86 to return to formerpositions.

After fracturing rock 86 to form all of the fissures 84, the fluid 82will pass through the fissures, carrying particles 10, which eventuallycollect in cavities or reach choke points. In the absence of theparticles 10, fissures 84 could close back up after the fracturing waterleaves. However, by containing the particles 10, the individualsubstrates 12 are themselves rock in the form of sand, ceramic sand, orthe like. Thus, a particle 10 need only obstruct the ability of thefissure 84 to close, and it may “prop” open the fissures 84 precludingthe rock 86 or the pieces of rock 86 from settling back into alignmentwith one another.

Thus, the particles 10 both alone and in collected piles act asproppants left behind by the fluid flow 82, by virtue of the particles10B captured. As a practical matter, it is only the substrate 12 thatacts as a proppant. The polymer 18 may eventually be worn off but caneasily be compressed, distorted, or cut. Regardless, as the fissures 84open, they are back filled and close in at choke points and settlingpoints collecting the substrate 12.

Referring to FIG. 7, a process 10 may include preparing 112 a fluid 82.Processing 114 other additives other than the particles 10 may be doneaccording to any suitable methods, including prior art processes. Adding116 directly to the fluid 82, the particles 10 as described hereinabove,may be done in such a manner that the operators need not wait forabsorption or any other processes to take place. Additional energy forelevating temperature is not required, neither mixing or the like, otherthan adding 116 directly particles 10 in to the flow 82. The flow 82will immediately grab the particles 10 according the principles of fluiddynamics in which fluid drag is dependent upon a shape factor of theparticle 10, the density of the fluid 82, the square of velocity of thefluid, and so forth, as defined in engineering fluid mechanics.

The fluid 82 now bearing the particles 10 would be immediately pumped118 into the formation 80 that is the reservoir 80 of 8 and oil field.Eventually, pressurizing 120 the reservoir by pressurizing the fluid 82results in creating 122 fractures 84 or fissures 84 within the formation80 by breaking up the rock 86 of the formation 80. A fracture 84 withenough displacement may make a site for material 10 to stagnate andcollect.

Creating 122 fracture lines throughout the formation 80 is followed bypenetrating 124, by the particles 10 borne in the fluid 82 into thepassages 84 or fissures 84 in the rock 86 of the formation 80. Wheneverthe flow 82 of fluid 82 carries a particle 10 to a choke point 108 in apassage 84, as illustrated in FIG. 6, a particle 10 will be lodged asillustrated in the inset of FIG. 6, a particle 10 with its polymer 18still secured and intact may be lodged. Similarly, the substrate 12 maybe lodged 126 and the polymer 18 may stripped therefrom by theconsequent or subsequent flowing of material in the flow 82. Likewise,piles of stagnant particles 10 may backfill spaces, precluding rock 86settling back in.

After the lodging 126 or propping 126 of the fissures 84 by thesubstrate 12, in the particles 10, the passages 84 will remain open.These fissures 84 may then be used tolater withdraw 128 the fluid 82from the formation 80. Thereafter, returning 130 the formation 80 toproduction may occur in any manner suitable. For example, heat may beadded to the formation, liquid may be run through the formation as adriver to push petroleum out, or the like.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrative,and not restrictive. The scope of the invention is, therefore, indicatedby the appended claims, rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed and desired to be secured by United States LettersPatent is:
 1. A method for forming proppant particles, the methodcomprising: providing a substrate, constituted as granules discrete fromone another; providing a synthetic binder comprising a first volume ofpolyacrylamide wetted with a solvent and absent any surfactant, and asecond volume of polyacrylamide in powdered form and absent anysurfactant; mixing the substrate granules with the synthetic binder sothat at least a portion of the substrate granules are at least partlycovered with the first volume of the synthetic binder; coating the atleast the portion of the substrate granules with the second volume ofthe synthetic binder to form polymer-coated substrate granules; anddrying at least a portion of the synthetic binder present on thepolymer-coated substrate granules, wherein, the polymer-coated substrategranules are able to flow in a carrier fluid.
 2. The method according toclaim 1, further comprising: removing from the polymer-coated substrategranules, in response to a pre-determined condition, at least a portionof the second volume of the synthetic binder.
 3. The method according toclaim 2, wherein the pre-determined condition is selected from: anamount of water absorbed by the second volume; a time of exposure of thesynthetic binder to water; a time of exposure of the second volume towater; an exposure of the substrate granules to friction from aformation; an exposure of the substrate granules to shear from thecarrier fluid; and exposure to a chemical.
 4. The method according toclaim 1, wherein the substrate granules comprise sand.
 5. The methodaccording to claim 2, wherein the at least a portion of the secondvolume is configured to form a gel when exposed to water.
 6. The methodaccording to claim 3, wherein the at least a portion of the secondvolume is configured to form a gel when exposed to water.
 7. The methodaccording to claim 1, wherein the polymer-coated substrate granules aredry and pourable prior to introduction into the carrier fluid.
 8. Amethod for forming proppant particles for use in a fissure, the methodcomprising: providing a substrate, constituted as granules discrete fromone another and having a hardness corresponding to that of a fissure;providing a synthetic binder comprising a first volume of polyacrylamidewetted with a solvent and absent any surfactant, and a second volume ofa water-absorbing polymer in powdered form and absent any surfactant;mixing the substrate granules with the synthetic binder so that at leasta portion of the substrate granules are at least partly covered with thefirst volume of the synthetic binder; coating the at least the portionof the substrate granules with the second volume of the synthetic binderto form polymer-coated substrate granules; drying at least a portion ofthe synthetic binder present on the polymer-coated substrate granules,wherein, the polymer-coated substrate granules are able to flow into thefissure by way of a carrier fluid and prop open the fissure; andremoving from the polymer-coated substrate granules, in response to apre-determined condition, at least a portion of the second volume of thesynthetic binder.
 9. The method according to claim 8, wherein thepre-determined condition is selected from: an amount of water absorbedby the second volume; a time of exposure of the synthetic binder towater; a time of exposure of the second volume to water; an exposure ofthe substrate granules to friction from a formation; an exposure of thesubstrate granules to shear from the carrier fluid; and exposure to achemical.
 10. The method according to claim 9, wherein thewater-absorbing polymer comprises polyacrylate.
 11. The method accordingto claim 9, wherein the substrate granules comprise an organicsubstrate.
 12. The method according to claim 9, wherein the substrategranules comprise sand.
 13. The method according to claim 9, wherein theat least a portion of the second volume is configured to form a gel whenexposed to water.
 14. The method according to claim 12, wherein thesynthetic binder is configured to adhere the at least a portion of thesecond volume to at least a portion of the sand.
 15. The methodaccording to claim 8, wherein the polymer-coated substrate granules aredry and pourable prior to introduction into the carrier fluid.
 16. Amethod for forming a polymer-coated substrate, the method comprising:providing a substrate, constituted as granules discrete from oneanother; providing a synthetic binder comprising a first volume ofpolyacrylamide wetted with a solvent, and a second volume of awater-absorbing polymer in powdered form; mixing the substrate granuleswith the synthetic binder so that at least a portion of the substrategranules are at least partly covered with the first volume of thesynthetic binder; coating the at least the portion of the substrategranules with the second volume of the synthetic binder to formpolymer-coated substrate granules; drying at least a portion of thesynthetic binder present on the polymer-coated substrate granules,wherein, the polymer-coated substrate granules are able to flow in acarrier fluid; and removing from the polymer-coated substrate granules,in response to a pre-determined condition, at least a portion of thesecond volume of the synthetic binder.
 17. The method according to claim16, wherein the pre-determined condition is selected from: an amount ofwater absorbed by the second volume; a time of exposure of the syntheticbinder to water; a time of exposure of the second volume to water; anexposure of the substrate granules to friction; an exposure of thesubstrate granules to shear from the carrier fluid; and exposure to achemical.
 18. The method according to claim 16, wherein thepolymer-coated substrate granules are dry and pourable prior tointroduction into the carrier fluid.
 19. The method according to claim18, wherein the synthetic binder is water-soluble and formed to have athickness on the substrate granules and a chemistry selected to completeat least one of: dissolving during transport of the substrate granulesthrough a formation; releasing the substrate granules from suspension inthe carrier fluid to lodge in the formation in response to at least oneof dissolving of the synthetic binder, dissolving of the polymercoating, and shearing of the polymer coating from the substrategranules.
 20. The method according to claim 16, wherein the syntheticbinder further comprises a third volume of a second polymer in powderform selected from a friction reducer, a biocide, an oxygen scavenger, aclay stabilizer, a scale inhibitor, and a gelling agent, and the thirdvolume is coated on the at least the portion of the substrate granulesin same manner and with the second volume.